1. Field of the Invention
The present invention relates to a support structure for a steering apparatus of an automotive vehicle.
2. Description of Related Art
Typically, automotive vehicle steering apparatus or systems of, for instance, the rack-and-pinion type have a steering gear box for converting rotary motion produced by a steering wheel into linear motion and transmitting it to wheels via tie rods so as to turn the wheels. The transmission of rotary motion of the steering wheel is connected to the gear box by means of a steering shaft and, if necessary, a relay rod or intermediate shaft. This steering shaft is typically held for rotation by and within a hollow steering column supported by parts of the vehicle body so as to orient appropriately the steering wheel toward the driver. Specifically, the steering column is supported at its lower or forward end portion directly or indirectly by a stationary part of the vehicle body, such as a dash panel, which is relatively weak in structural rigidity, and at its middle portion directly by a support member comprising, for instance, a hollow steel pipe extending transversely between and secured to side members, such as front pillars, of the vehicle body which have high rigidity. This kind of steering apparatus support structure includes a mechanism for allowing the steering column to be displaced downward as the forward portion of the steering column is forced backward during a frontal end collision so as to prevent the steering wheel from being displaced upward and backward toward the driver. Such a steering apparatus support structure is known from, for instance, Japanese Unexamined Patent Publication No. 3-567.
The steering apparatus support structure described in the publication mentioned above is insufficient in structural rigidity against oscillating external impacts which produce up and down positional changes of where the steering wheel is installed.
Another type of steering system support structure includes a connecting member which connects a steering column with a rigid, stationary support member or structure, such as a hollow steel pipe, disposed immediately after a dashboard by which an engine compartment and a passenger compartment are separated and which supports an instrument panel. This rigid support member is hereafter referred to as an instrument panel support member or structure for simplicity.
With apparatus support structure of this kind, in the event of first or primary frontal end collisions, various devices, such as an engine and a powertrain, placed inside the engine compartment are forced backward and, sometimes, push the dashboard and instrument panel. Such backward positional displacement of the dashboard and instrument panel forces the steering column with the steering wheel, which is secured to the instrument panel support member, backward. Such a primary frontal end collision is often accompanied by what is called a secondary collision in which the driver is thrown forward due to an impact and hits instruments in front of the driver immediately after the occurrence of a frontal end collision. If the steering wheel has been forced backward upon the primary frontal end collision, the driver hits strongly the steering wheel during the secondary collision, resulting in serious bodily injury or damage.
In order to avoid such a secondary collision, a collapsible type of steering shaft apparatus is described in, for instance, Japanese Utility Model Publications Nos. 3-27899 and 3-56455, and some of them have been put into the market. Such a collapsible steering shaft support structure includes mechanical connecting or linking members: namely a first connecting or linking member for mechanically connecting a support bracket secured to a deformation free component of the vehicle body (the term "deformation free component" used herein shall mean and refer to a component or part of the vehicle body very hard to be deformed by an external impact due to frontal end collisions) and an instrument panel support member together, and a second connecting or linking member for mechanically connecting the steering column and the support bracket together. The first connecting member is designed and adapted to allow the support bracket to be disconnected easily from the instrument panel support member when a relative backward movement occurs between the support bracket and instrument panel support member. Similarly, the second connecting member is designed and adapted to allow the steering column to be disconnected easily from the support bracket when a relative forward movement occurs between the steering column and support bracket.
With the typical steering apparatus equipped with such a collapsible structure, when the instrument panel support member is forced backward due to a primary frontal end collision, the mechanical connection is broken between the instrument panel support member and support bracket, preventing the steering shaft, and hence the steering wheel, from being forced backward. In addition, if the driver is thrown forward and hits the steering wheel during a secondary collision, the steering column is forced forward by the driver and disconnected from the support bracket and, as a result, allowed to be further displaced forward by the driver. This forward displacement of the steering column enhances absorption of the energy of an impact before it has a considerable effect on the driver.
However, with the steering apparatus support structure of this kind, when an external impact is exerted somewhat obliquely upward on the instrument panel support member through the dashboard upon the occurrence of an frontal end collision, it is hardly effective for the first connecting member to disconnect the mechanical linkage of the support bracket from the instrument panel support member. In this event, the supporting bracket is forced backward being accompanied with the instrument panel support member, and is accordingly displaced backward relatively to the steering column. Viewing this movement from the side of the steering column, the steering column is displaced forward relatively to the support bracket. As a result, the second connecting member possibly breaks the mechanical linkage of the steering column with the support bracket during a primary frontal end collision. If in fact the mechanical linkage by the first connecting member is broken during a primary frontal end collision, the steering column and/or the steering wheel is hardly held steady in position, leading to ineffective operation of an air bag as a supplemental restraint system to the driver. Further, in the event of a frontal end collision, if a considerably strong external impact is exerted on the foremost part of the steering apparatus, such as the gear box, the steering shaft is forced backward, possibly making the steering wheel interfere with the driver.
In addition, it is of overriding importance today that these steering systems can be assembled in vehicles with high working efficiency. For the purpose of providing a brief background that will enhance an understanding of the troublesome installation of conventional steering systems in vehicles, reference is made to FIGS. 1 to 3.
Referring to FIG. 1, in order to provide steady support of a steering shaft assembly 51, including a steering column, a steering shaft rotatively received in the steering column and a steering wheel, the assembly 51 is fixedly attached at its lower or forward and upper or rearward portions to a bracket 52 which is assembled to the vehicle body by, on one hand, mounting the bracket 52 on a rigid support beam 53 extending transversely between rigid side members of the vehicle body, such as front pillars (not shown), and, on the other hand, bolting, or otherwise securing, the front half portion of the bracket 52 to a cowl panel 54 which is one of stationary rigid components of the vehicle body. When the steering shaft assembly 51 with the bracket 52 attached previously thereto is placed in position into the vehicle body, it is hard to place the steering shaft assembly 51 in the vehicle body without any interference of the bracket 52 with structural components of the vehicle body. Specifically, before assembling of the steering shaft assembly 51 into the vehicle body, the bracket 52 is mounted on the rigid support beam 53 first and then the steering shaft assembly 51 is secured to the bracket 52.
After having preparatorily assembled an instrument panel 55 to the steering shaft assembly 51 thus pre-assembled to the bracket 52 and support beam 53 as one whole as shown in FIG. 2, the whole assembly is placed inside the vehicle body. During placing the whole assembly, a pair of stay arms 56 extending downward from the support beam 53 are linked to a pair of counter stay arms 58 extending upward from a floor panel (not shown) by means of the engagement between a link pin 57 and a slot-like opening 59 provided on each pair of the stay arms 56 and 58. After the completion of this provisional installation, the whole semi-assembled steering shaft assembly 51 including the support beam 53 is turned upward about the link pins 57 and changed in location from a preparatory position indicated by a solid line to a fitting position indicated by a dotted line in FIG. 2. During changing of the semi-assembled steering shaft assembly 51 in location, the movement of the bracket 52 along a line indicated by a reference character .alpha. makes the bracket 52 interfere at its forward end with the cowl panel 54, so as to cause a decline in the efficiency of installation of the steering shaft assembly 51.